Field-based evaluation of trunk strength using a novel in-chair assessment system in elite wheelchair athletes

Trunk strength is essential for performance in wheelchair-based sports, yet assessment under sport-specific conditions is challenging. The athlete and their sport wheelchair act as a unit, so meaningful assessment should occur in the wheelchair itself. We developed a mobile device that measures isometric trunk flexion, extension, and lateral flexion directly in the athlete’s own sport wheelchair. We first examined test-retest reliability in both able-bodied participants and elite wheelchair basketball (WB) players. Both cohorts showed high day-to-day consistency (intraclass correlation coefficient, 0.85–0.97; coefficient of variation, < 10%). We then demonstrated that trunk forces measured distinguish between established WB functional classes 1.0 (high impairment) – 4,5 (low impairment). Higher classified groups produced significantly greater forces, with a strong positive correlation between classification and force (r = 0.76–0.87). Next, classification-specific reference values were generated and compared with measures from able-bodied participants. Lower classified athletes (1.0-3.5) produced approximately 56% less trunk force than able-bodied participants, whereas players in the highest classification (4.0-4.5) demonstrated comparable or up to 31% higher force in trunk flexion. These findings support the device as a reliable, field-based method to quantify trunk strength in athletes’ own wheelchairs and show that it can differentiate functional classes, enabling its application in performance testing.